1. Field of the Invention
The present invention relates to a sensor including a resistor formed on a substrate and detecting a predetermined physical quantity. More particularly, the present invention relates to a physical quantity sensor which is applied to, for example, a flow sensor for detecting the flow rate of a fluid, an acceleration sensor, and an inclination sensor.
2. Description of the Related Art
As a flow sensor for detecting an intake air amount in an internal combustion engine such as an automobile, it is proposed to manufacture a sensor device on a semiconductor substrate made of, e.g., silicon (Si) by using the micromachining technology. That type of flow sensor is advantageous in that it can be mass-produced at a low cost, has a small size, and can be driven with low electric power. That type of flow sensor is mainly practiced as an air flow sensor employing a heating resistor, which can directly measure a mass flow rate.
In known heating-resistor flow sensors of semiconductor type, as disclosed in, e.g., Patent Document 1 (JP,A 2001-021401), a silicon substrate is partly removed to form a diaphragm structure having a cavity, and a heating resistor and a temperature compensation resistor are formed on the diaphragm. The sensor of such a structure has the problem that the mechanical strength is low and flexion may occur due to unbalance among internal stresses in a diaphragm section. According to the technique disclosed in Patent Document 1, a rigid member is disposed in the diaphragm section to suppress flexion of the diaphragm, thereby improving reliability of a sensor device and increasing accuracy in measurement of the air flow rate.